I second this recommendation! Frame manufacturers sometimes call these products "museum glass", which combines anti-reflective properties with UV filters, usual

I second this recommendation! Frame manufacturers sometimes call these products "museum glass", which combines anti-reflective properties with UV filters, usually with price points at 70% and 92% filters. Some E-ink panels can be somewhat susceptible to UV light and perform better under a filter. You will sometimes find warnings in data sheets about refresh performance in direct sunlight, and danger of long-term permanent damage. Some of E-ink's signage products have, I think, filter layers built-in. But also if you're using a passepartout like in this project, and the frame will hang in sunlight and you're not sure how the paper will perform, it's worth springing for the UV protection to avoid yellowing over time.